Speaking about the first round of negotiations between the UK and EU in June, the document said Barnier "observed that the United Kingdom had not yet really engaged in the negotiations or spelled out its positions".

The minutes went on: "He noted in this regard that David Davis, the Secretary of State for Exiting the European Union, did not regard his direct involvement in these negotiations as his priority and there was also a possibility that he might not be present at the full opening session of the July cycle of talks."

According to the minutes, Juncker "expressed his concern about the question of the stability and accountability of the UK negotiator [Davis] and his apparent lack of involvement, which risked jeopardising the success of the negotiations.

“He invited Barnier to remain firm on this point and not to accept discussions at the purely technical level with negotiators who had no political mandate, while fundamental political questions still remained."

The exchanges are the latest evidence of the strains which have emerged between the British and European negotiating teams.

At a tense press conference last week, Barnier said Britain's refusal to accept it had to pay a so-called 'divorce bill' when it leaves the EU meant there was a lack of "trust" between the two sides.

Davis hit back at the weekend when he appeared to call his opposite number "silly" for saying insufficient progress had been made in the talks so far.

But speaking at another press conference in Brussels today, Barnier insisted his relationship with Davis was good.

He said: "I have good relations with him still, and good professional relations.

“Seven days ago exactly at this time we arrived at the end of the third round of negotiations and David Davis was standing here and I paid tribute to his professionalism and the competence of the whole of the UK team and I have nothing further to add on that point."